Clutch control to enter powersplit hybrid powertrain parallel mode

ABSTRACT

A selectively actuatable one-way clutch is controlled to brake or release a generator such that a powersplit hybrid powertrain enters or exits a parallel mode of operation. To brake the generator and enter the parallel mode, the clutch is activated while overrunning the generator before the generator is slowed to engage the clutch. To release the generator and exit the parallel mode, the generator is controlled to overrun the clutch before deactivating the clutch and returning the generator to a base speed control.

BACKGROUND OF INVENTION

The present invention relates to a method of controlling an automotivepowertrain and in particular to using a selectively actuatable one-wayclutch to enter and exit a parallel mode of operation for a powersplitpowertrain.

An automotive vehicle may use a powersplit hybrid electric powertrain.Included in the powersplit powertrain is an electric generator, whichmay also alternatively operate as an electric motor. The powersplitpowertrain may be operated in a plurality of modes, including negativepowersplit, positive powersplit, and parallel modes. In the positivepowersplit mode the generator operates and produces electrical power. Inthe negative powersplit mode the generator consumes electrical power andproduces a torque to propel the vehicle. In the parallel mode thegenerator neither produces nor consumes electrical power, which allowsthe vehicle to be propelled by a combined torque produced by the engine,a second electric motor, and braking of the generator. Typically, afriction clutch is used to brake the generator so that the powertrainmay enter the parallel mode.

However, time required to brake the generator to enter the parallel modereduces fuel efficiency for the powersplit powertrain. The frictionclutch may require a hydraulic system with a pump to maintain pressureto keep the friction clutch braking the generator. The pump creates anadditional load on the powertrain and may further reduce fuelefficiency.

SUMMARY OF INVENTION

An embodiment contemplates a method of controlling a powersplit hybridvehicle powertrain. A generator is rotated to overrun a selectivelyactuatable one-way clutch coupled to the generator. The clutch iselectronically activated while overrunning. The generator is slowed toengage the activated clutch. The clutch is engaged when the generatorhas slowed to an engagement speed. Torque is transferred from thegenerator to the engaged clutch before turning off the generator.

Another embodiment contemplates a method of controlling a powersplithybrid vehicle powertrain of a vehicle. A stopped generator is turned onwhile a selectively actuatable one-way clutch coupled to the generatoris activated and engaged. The stopped generator is rotated in adisengagement direction to overrun and disengage the clutch. The clutchis deactivated while overrunning.

An advantage of an embodiment is expediting control of the one-wayclutch when the powersplit powertrain enters a parallel operating mode.This improves fuel efficiency for a vehicle using the powersplitpowertrain.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic view of a hybrid electric powertrain.

FIG. 2 is a schematic, perspective view of a one-way clutch.

FIG. 3 is a schematic view of a portion of the one-way clutch.

FIGS. 4A and 4B are a flow chart of a control routine for a hybridelectric powertrain.

DETAILED DESCRIPTION

FIG. 1 schematically illustrates a powersplit type hybrid electricpowertrain 10 for an automotive vehicle 12. The powertrain 10 is merelyexemplary, and may take other forms, such as front wheel drive, rearwheel drive, and all wheel drive types of powertrains.

The powertrain 10 includes an internal combustion engine 14 powering acrankshaft 16. The crankshaft 16 transmits torque from the engine 14 toa planetary gear set 18. Also connected to transmit torque to and fromthe planetary gear set 18, via a generator shaft 20, is a generator 22.The planetary gear set 18 comprises a sun gear, ring gear, and carrierassembly, which can be conventional and so the specifics of this gearset are omitted from FIG. 1 for clarity. The crankshaft 16 connects tothe carrier assembly and the generator shaft 20 connects to the sungear. The ring gear transmits torque, via a first gearing input 24, to agearing 26. Also connected to the gearing 26, via a second gearing input28, is an electric motor 30. The generator 22 and the motor 30 areconnected via a high voltage bus 32 to a battery 34. The generator 22 isalso connected via a brake shaft 36 to a selectively actuatable one-wayclutch (OWC) 38. The gearing 26 transmits torque via a gearing output 40to a differential 42. The differential 42 transmits torque, via firstand second axles 44 and 46, respectively, to rotate first and secondwheels 48 and 50, respectively. Operation of the powertrain 10,including the engine 14, generator 22, motor 30, and one-way clutch 38,is controlled by a controller 52. The controller 52 may be a vehiclespeed controller (VSC), which controls the powertrain 10 to regulate aspeed of the vehicle 12.

As described, the powertrain 10 may operate in a positive powersplitmode in which the generator 22 operates and produces electrical power.For example, electrical current produced by the generator 22 may powerthe motor 30 or charge the battery 34. Alternatively, the powertrain 10may operate in a negative powersplit or parallel mode. In the negativepowersplit mode the generator 22 consumes electrical power to rotate andproduce a generator torque that propels the vehicle 12. For example,electrical power consumed by the generator 22 may come from the motor 30(operating to generate electric power) or the battery 34. In theparallel mode the generator 22 neither produces nor consumes electricalpower. The powertrain 10 operates in the parallel mode when the one-wayclutch 38 brakes the generator 22 from rotating. Once braked fromrotating, and having torque transferred to the clutch 38, the generator22 may be turned off. In the parallel mode, torque is supplied to thegearing 26 from the engine 14 and the motor 30. The parallel mode allowsboth the engine 14 and the motor 30 to propel the vehicle 12.

FIG. 2 illustrates the one-way clutch 38. The one-way clutch 38comprises a rocker plate 100 having pockets 108 that each contain acorresponding rocker 102, which are pivotally hinged within the pockets108. The clutch 38 also includes a cam plate 104, which has a pluralityof notches 112 that define teeth. The teeth can selectively catchfingers extending from the rockers when the rockers 102 are pivoted toextend the fingers radially inward. The rocker plate 100 is connected toand rotates with the brake shaft 36, and the cam plate 104 is secured tothe vehicle 12 to prevent rotation of the cam plate 104. For example,the cam plate 104 may be bolted to a casing for the clutch 38.

The cam plate 104 contains a coil 106 that may be selectively energizedto produce a magnetic force. As illustrated in FIG. 2, the clutch 38 isin a deactivated state, in which the fingers of the rockers 102 arepivoted to a radially outer position in the rocker plate recesses andthus the fingers do not engage the teeth of the cam plate 104. When theclutch 38 is in the deactivated state, the rockers 102 fit within thepockets 108 without protruding beyond a radially inside face 110 of therocker plate 100. The rockers are biased by a spring 120 to remainwithin the pockets 108 without protruding (a bias in a counterclockwisedirection as illustrated in FIGS. 2 and 3). When the clutch 38 isdeactivated (i.e., the coil 106 is not energized), no torque istransferred between the rocker and cam plates 100 and 104, respectively.The clutch 38 is activated by energizing the coil 106. The magneticforce that results from electrifying the coil 106 pivots the fingers ofthe rockers 102 out of the pockets 108, against the bias of the spring120, such that the fingers protrude beyond the radially inside face 110of the rocker plate 100.

As understood by one skilled in the art, the rockers 102 mayalternatively be hinged from the cam plate 104, the pockets 108correspondingly located in the cam plate 104, the notches 112 located inthe rocker plate 100, and the coil 106 located in the rocker plate 100.

FIG. 3 illustrates the clutch 38 in an activated state. The fingers ofthe rockers 102 extend beyond the inside surface 110 of the rocker plate100 and are pivotally biased towards the notch 112 of the cam plate 104.As discussed, the clutch 38 is a selectively actuatable one-way clutch.When the clutch 38 is activated and the rocker plate 100 rotates in adisengagement direction 114, the fingers of the rockers 102 will becammed outward by the teeth and so will not engage with the teeth toprevent rotation. Rather, as the rocker plate 100 rotates, a pluralityof first cam surfaces 116 deflect the fingers of the rockers 102 towardthe pockets 108.

Alternatively, when the clutch 38 is activated and the rocker plate 100attempts to rotate in an engagement direction 122, opposite thedisengagement direction 114, the fingers of the rockers 102 engage witha second engagement surface 118 of the teeth and the clutch 38 isengaged. The mechanical engagement between the cam and rocker plates 104and 100, respectively, prevents rotation of the rocker plate 100. Themechanical engagement is sufficient such that, if the coil 106 of theclutch 38 is deactivated, the clutch 38 remains engaged to preventrotation. De-energizing the coil 106 once the clutch 38 is engaged,which deactivates the rockers 102, reduces discharge of the battery 34while still preventing rotation of the rocker plate 100. Since therocker plate 100 is rotationally fixed to the generator 22, braking therocker plate 100 from rotating also prevents the generator 22 fromrotating.

Rotation of the rocker plate 100 may be changed from the disengagementdirection 114 to the engagement direction 122 by slowing rotation in thedisengagement direction 114 to a second stop before commencing rotationin the engagement direction 122. Rotation in the engagement direction122 may then be accelerated from the second stop to the desired speed.Rotation of the rocker plate 100 may be changed from the engagementdirection 122 to the disengagement direction 114 by slowing rotation inthe engagement direction 122 to a stop before commencing rotation in thedisengagement direction 114. Similarly, rotation in the disengagementdirection 114 may then be accelerated from the stop to a desired speed.A time period between stopping and commencing rotation of the rockerplate 100 may vary and may be minimized so as to be imperceptible to adriver of the vehicle 12.

The engaged clutch 38 may be disengaged by rotating the rocker plate 100in the disengagement direction 114. With or without the coil 106 of theclutch 38 being activated, when the rocker plate 100 is rotated in thedisengagement direction 114, no engagement occurs between the rocker andcam plates 100 and 104, respectively, thus allowing the rocker plate 100to freely rotate. When the coil 106 of the clutch 38 is deactivated,allowing the springs to pivot the fingers away from engagement with theteeth, the rocker plate 100 may be freely rotated in the disengagementdirection 114 and engagement direction 122.

FIGS. 4A and 4B will now be discussed with reference to FIGS. 1-3. FIGS.4A and 4B illustrates a control routine 200 for the powertrain 10 whenentering or exiting the parallel mode.

In a step 202, the controller 52 receives a command to enter theparallel mode. The controller 52 determines, in a step 204, whetherconditions are acceptable to enter the parallel mode. One such conditionis that the entry command has not been cancelled or overridden. Forexample, a command to exit the parallel mode would override the entrycommand. Other conditions may include one or more of the following: thatthe engine 14 is delivering a requested torque through an engine powerPI (proportional, integral) controller; the engine 14 is operating in apower range that will produce efficiency gains from entering theparallel mode; actual and commanded speeds of the engine 14 are close toan engagement speed for engaging the one-way clutch 38; the actual andcommanded speeds of the engine 14 are above a lug limit speed forminimizing noise, vibration, and harshness effects; or discharge limitsand a state of charge for the battery 34 are within nominal ranges. Ifthe conditions are not acceptable, generator 22 returns to a base speedcontrol routine in a step 206. If the conditions are acceptable, in astep 208, the generator 22 is rotated in the disengagement direction 114to overrun the clutch 38. The conditions are monitored throughout theroutine 200.

Following the step 208, the conditions are again verified to beacceptable in a step 210. If the conditions are no longer acceptable,the generator 22 is rotated toward a desired speed in a step 212 beforethe step 206. If the conditions continue to be acceptable, thecontroller 52 determines in a step 214 if a current speed of thegenerator is greater than an activation speed for the clutch 38. Theactivation speed is a speed at which the generator 22 is overrunning theclutch 38—i.e., the rocker plate 100 is overrunning the cam plate 104 inthe disengagement direction 114. Exceeding the activation speed mayrequire rotation of the generator 22 be changed from the engagementdirection 122 to the disengagement direction 114. If the current speedis not greater than the activation speed, then the routine 200 returnsto the step 208. If the generator speed is greater than the clutchactivation speed, then in a step 216, the clutch 38 is activated. Thegenerator 22 is then slowed from overrunning to the engagement speed.The engagement speed may be zero or close to zero.

The generator 22 may rotate to the activation speed to overrun theclutch 38, the clutch 38 activates, and then the generator 22 slows fromthe activation speed to the engagement speed. Alternatively, thegenerator 22 may rotate to overrun the clutch 38 at a peak overrunningspeed, the generator 22 slows from the peak overrunning speed to theactivation speed, the clutch 38 activates, and then the generator 22slows from the activation speed to the engagement speed. Increasing thepeak overrunning speed additionally ensures the generator 22 isoverrunning the clutch 38. Setting the activation speed at less than thepeak overrunning speed delays activation of the clutch 38. Delayedactivation of the clutch 38 avoids, when the conditions are no longeracceptable, needing to deactivate the clutch 38 prior to the generator22 being returned to the base speed control routine.

As the generator 22 is slowing to the engagement speed, in a step 220,verification is made that the conditions remain acceptable. If theconditions are not acceptable, the clutch 38 is deactivated in a step222 before the steps 212 and 206. If the conditions remain acceptable,the routine 200 proceeds to a step 224.

Just prior to when the clutch 38 is engaged to transfer torque from thegenerator 22, a current torque for at least one of the generator 22 orthe clutch 38 may be recorded in a step 224. The recorded torque may beused in a feed forward term of a torque computation for controlling, inpart, the generator 22. The feed forward term uses the torque recordedin the step 224 to predict a torque required to produce the desiredspeed. For example, the torque recorded in the step 224 may be used toset a starting torque for returning the generator 22 to the base speedcontrol routine after a condition is found to be unacceptable. In thestep 226, the clutch 38 is engaged and, in a step 228, torque istransferred from the generator 22 to the clutch 38 to brake thegenerator 22 to a stop. Once the generator 22 is braked to a stop, theparallel mode is active.

In a step 230, verification is made that the conditions remainacceptable. If the conditions are not acceptable, the recorded torque isused in the feed forward term to control rotation of the generator 22before the steps 232, 234, 222, 212, and 206. If the conditions remainacceptable, the generator 22 is turned off in the step 236.

An additional verification of the conditions occurs in a step 238. Ifthe conditions are not acceptable, the generator 22 is turned on in astep 240 before the steps 232, 234, 222, 212, and 206. If the conditionsare acceptable, then the clutch 38 may be deactivated in a step 242.Deactivating the clutch 38 after the generator is braked and turned offconserves charge of the battery 34. The clutch 38 may be deactivatedwhen the clutch 38 is mechanically engaged with the generator 22.

After the clutch 38 is deactivated, the control routine 200 returns tothe step 238 to monitor that the conditions remain acceptable. Asdiscussed, the command to exit the parallel mode would be anunacceptable condition. Alternatively, if the step 242 is not includedin the control routine 200, when conditions are acceptable in the step238, the control routine 200 may iterate the step 238 to monitor thatconditions remain acceptable.

While certain embodiments of the present invention have been describedin detail, those familiar with the art to which this invention relateswill recognize various alternative designs and embodiments forpracticing the invention as defined by the following claims.

The invention claimed is:
 1. A method of controlling a powersplit hybridvehicle powertrain comprising: rotating a generator to overrun aselectively actuatable one-way clutch coupled to the generator;electronically activating the clutch while overrunning; slowing thegenerator to engage the activated clutch; engaging the clutch when thegenerator has slowed to an engagement speed; transferring torque fromthe generator to the engaged clutch before turning off the generator. 2.The method of claim 1 in which activating the clutch comprises pivotingfingers of rockers in a rocker plate outward from the rocker plate byenergizing a coil in a cam plate to produce a magnetic force, the rockerplate being connected to the generator and the cam plate being securedto prevent rotation of the cam plate.
 3. The method of claim 2 in whichrotation of the clutch in the disengagement direction does not transfertorque between the rocker and cam plates and rotation in an engagementdirection, opposite the disengagement direction, transfers torquebetween the rocker and cam plates when the clutch is activated and doesnot transfer torque between the rocker and cam plates when the clutch isdeactivated while disengaged.
 4. The method of claim 2 in which landingthe clutch comprises the fingers mechanically engaging with engagementsurfaces of the cam plate.
 5. The method of claim 3 in which, afterturning off the generator while the clutch is engaged, the rockersremain mechanically engaged with the cam plate.
 6. The method of claim 5in which, after turning off the generator, the clutch is deactivated. 7.The method of claim 1 further comprising deactivating the clutch andoperating the generator under a base speed control routine after acondition is found to be unacceptable while the generator is overrunningthe activated clutch.
 8. The method of claim 1 further comprisingaccelerating the generator to overrun the clutch before deactivating theclutch and operating the generator under a base speed control routineafter a condition is found to be unacceptable when the clutch isengaged.
 9. The method of claim 1 further comprising recording at leastone of a generator torque or a clutch torque, prior to transferringtorque from the generator to the clutch, to set a starting torque forreturning the generator to a base speed control routine after acondition is found to be unacceptable.
 10. The method of claim 1 inwhich the engagement speed is zero.